A photographic process utilizing a silver halide has heretofore been widely used due to its excellent photographic characteristics such as sensitivity, control of gradation, etc., as compared with other photographic processes such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation processes for light-sensitive materials using a silver halide, a technique capable of easily and quickly obtaining an image, for example, a dry development process such as a process using heat, has been developed for the conventional wet development process using a developing solution.
Heat-developable light-sensitive materials are known in the art. Heat-developable light-sensitive materials and processes suitable therefor are described in, for example, Shashin Kogaku no Kiso, Corona Co., Ltd. pages 553-555, Eizo Joho, April 1978, page 40, Nebletts, Handbook of Photography and Reprography, 7th ed., Van Nostrand Reinhold Company, pages 32-33, U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, June 1978, pages 9-15 (RD-17029).
Various processes for obtaining color images using a dry process have been proposed.
With respect to processes for forming color images by the reaction of an oxidation product of a developing agent with a coupler, use of a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as disclosed in U.S. Pat. No. 3,531,286, p-aminophenol type reducing agent as disclosed in U.S. Pat. No. 3,761,270, a sulfonamidophenol type reducing agent as disclosed in Belgian Pat. No. 802,519 and Research Discosure, pages 31-32 (September, 1975) and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as disclosed in U.S. Pat. No. 4,021,240 has been proposed.
These processes, however, are disadvantageous in that turbid color images are formed, because a reduced silver image and a color image are simultaneously formed in the exposed area after heat-development. In order to eliminate these disadvantages, a process which comprises removing a silver image by liquid processing and a process which comprises transferring only the dye to another layer, for example, a sheet having an image receiving layer have been proposed. However, the latter process is not desirable because it is not eady to transfer only the dye as opposed to unreacted substances.
Another process which comprises introducing a nitrogen containing heterocyclic group into a dye, forming a silver salt and releasing a dye by heat-development has been proposed in Research Disclosure, RD-16966, pages 54-58 (May, 1978). With this process, clear images can not be obtained because it is difficult to control the release of dyes from the non-exposed areas, and thus it is not a generally applicable process.
Further, processes for forming a positive-working color image by a silver dye bleach process utilizing heat as well as useful dyes therefor and methods for bleaching are disclosed in, for example, Research Disclosure, RD-14433, pages 30-32 (April, 1976), ibid., RD-15227, pages 14-15 (December, 1976) and U.S. Pat. No. 4,235,957.
However, these processes require an additional step and an additional meterial for accelerating a bleaching of the dyes, for example, a step of heating with a superposed sheet with an activating agent. Furthermore, they have the disadvantage that the resulting color images are gradually reduced and bleached by free silver which is also present during storage for a long period of time.
Moreover, a process for forming a color image utilizing a leuco dye has been disclosed in, for example, U.S. Pat. Nos. 3,985,565 and 4,022,617. This process is, however, disadvantageous in that it is difficult to incorporate the leuco dye in the photographic material in a stable manner and coloration gradually occurs during storage.
In addition, all of the above-described conventional processes generally require long periods of time for development and the resulting images have high fog and low density.
In order to overcome the above-described disadvantages, many improved processes for color image formation have been porposed, in which a mobile dye is imagewise released by the oxidation-reduction reaction between a light-sensitive silver halide and a dye releasing redox compound and the released mobile dye is transferred to a dye fixing layer, as disclosed in EP Patent Publications Nos. 76,492 and 79,056 and Japanese patent application (OPI) Nos. 149046/83 and 149047/83.
In one such image formation process, a dye fixing material having a dye fixing layer is brought into contact with a light-sensitive material, thereby the imagewise formed mobile dye is transferred into the dye fixing layer. According to this process, the dye fixing layer should be peeled apart from the light-sensitive material after the dye is transferred. Therefore, the dye fixing material must have surface properties such that it adheres to the light-sensitive material intimately enough to allow thorough transferring of the mobile dye; movement of the dye is not interfered with; it can be peeled off smoothly after heating; and the surface of the dye fixing layer is not roughened upon peeling off.
With respect to the peeling property or separability of dye fixing materials, various proposals for color diffusion transferring materials have been made, and those using a hydrophilic polymer on the surface are known. However, since the above-described image formation process involves heating at 60.degree. C. or higher temperatures for dye transferring, if gelatin, polyvinylpyrrolidone, etc., commonly employed are used on the surface, it becomes quite difficult to peel the dye fixing material from the light-sensitive material and forced separation would result in a damage of the surface of the dye fixing material.